1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, it relates to a control of allowing an external power source, such as a commercial power source or the like, and an additional auxiliary power source to supply electric power to a fixing heater to heat a fixing section.
2. Description of the Related Art
There has been an image forming apparatus, such as a copying machine, in which both a commercial power source and an auxiliary power source (for example, an electric double layer capacitor) apply a high current to a fixing heater to heat a fixing roller such that a length of time taken for raising the temperature of the fixing roller to a predetermined fixing temperature is shortened when the image forming apparatus is in an initial stage of starting up or when the image forming apparatus is restored form an energy-saving mode of suspending an electric power supply to the fixing heater and waiting for a printing operation (refer to Japanese Patent Unexamined Publication No. 10-282821). According to such image forming apparatus in which both the commercial power source and the auxiliary power source supply electric power to drive the fixing heater, the temperature of the fixing roller is raised in a short period of time, and the fixing roller is allowed to wait at a low temperature in the energy-saving mode. Accordingly, it is effective for saving electric power.
However, in such image forming apparatus described above, both the commercial power source and the auxiliary power source always apply a high current to the fixing heater to heat the fixing roller when the image forming apparatus is in an initial stage of starting up or restores from the energy-saving mode. Therefore, an effect of saving an electric power can be obtained in view of overall consumption of electric power for driving the image forming apparatus. However, in view of focusing only on energy consumption in the initial stage of starting up or restoration from the energy-saving mode, consumption of electric power becomes greater than the case where only the commercial power source supplies electric power to drive the fixing heater. Further, the number of times of charging and discharging an auxiliary power source composed of an electric double layer capacitor increases, and this increase causes a problem of a negative effect on a life of the auxiliary power source.